This invention is directed to an air bag gas generator and air bag system for protecting a passenger from impacts, and in particular, a gas generator for an air bag using an igniting means which includes an initiator that is activated by an electrical signal.
An air bag system is attached to a vehicle, such as an automobile, etc., for the purpose of protecting a passenger from an impact due to a collision. In this air bag system, when a sensor detects an impact, a gas generator is activated, and a cushion (air bag) is formed between the passenger and the vehicle. The gas generator is activated in such a way that the sensing of the impact by the impact sensor activates igniting means, causing gas generating means to burn and generate a combustion gas. Conventionally, for such a gas generator, there are a mechanical ignition type gas generator, which is activated by sensing an impact exclusively by means of a mechanical method, and an electrical ignition type gas generator, which is activated by an electrical signal transmitted from an impact sensor, such as a semiconductor-type acceleration sensor, etc., that senses an impact.
Among these gas generators, in the electrical ignition type gas generator, in particular, the signal from the electrical sensor upon detection of an impact, is transmitted via a lead wire to an initiator which is contained in the housing. The initiator is activated by the electrical signal to ignite and burn an enhancer. The flame from the burning enhancer ignites and burns gas generating means to generate combustion gas. Also, the initiator may, in some cases, directly ignite and burn the gas generating agents instead of the enhancer. The combustion gas generated in the housing flows into the air bag from gas discharge ports provided in the housing. Therefore, in the electrical ignition type gas generator, it is necessary for the initiator, which is contained in the housing and actually activates the gas generator, to be connected to the electrical sensor, which senses the impact and outputs a signal, provided outside the housing.
However, the lead wire extending from the initiator has a directional property. Therefore, in the conventional gas generator for an air bag, the lead wire would be slack or too short depending on the direction which the initiator has been installed, causing the lead wire to be too short for connecting to the electrical sensor.
The present invention solves these problems found in the above-mentioned conventional air bag gas generator and provides an air bag gas generator which ensures that the length of the lead wire is sufficient, even if the length of the connector in the air bag gas generator is predetermined, when installing this gas generator in the module.
The air bag gas generator according to the present invention is characterized in that it uses igniting means having an initiator, which is exclusively activated by an electrical signal and by installing the ignitor in the housing after the initiator has been positioned.
That is, the air bag gas generator of the present invention comprises, in a housing having gas discharge ports and an igniting means storage hole: igniting means activated by an impact; gas generating means ignited by the igniting means and burns and generates a combustion gas; and a coolant/filter, which cools the combustion gas and/or collects the combustion residue; and by having the igniting means composed to include an initiator which is activated by an electrical signal, with the initiator being positioned and then installed in the housing.
The positioning of the initiator can be done, for instance, by forming a positioning portion in the initiator collar, to which the lower portion of the initiator is fitted, forming, in an insertion jig for inserting the initiator, an engaging portion which engages the positioning portion in the initiator collar, and engaging the positioning portion of the initiator collar with the engaging portion in the insertion jig. Such a positioning portion can be obtained by forming a step helix by cutting a portion of the bottom surface of the initiator collar into a step helix form in the radial direction while retaining the edge portion thereof, or by forming a groove by cutting a portion of the bottom surface of the initiator collar in the radial direction. Especially, when the positioning portion is formed by cutting a portion of the bottom surface of the initiator collar into the step helix form in the radial direction, while retaining the circumference of the initiator collar, the air bag gas generator which utilizes the initiator can, even when in operation, more securely and advantageously prevent the leakage of the combustion gas from any gap between the inner surface of the portion containing the initiator and the outer circumferential surface of the initiator collar.
The engagement between the positioning portion of the initiator collar and the engaging portion of the insertion jig is achieved, for instance, by: forming the engaging portion of the insertion jig as a fitting protrusion which complementarily fits in the positioning portion formed as described above; complementarily fitting the fitting protrusion to the above-mentioned positioning portion; and disposing the initiator in the housing while positioning it. When a gas generator attachment portion, which attaches the air bag gas generator to a module case, is formed in the housing and the initiator is positioned with respect to the gas generator attachment portion, it is possible to position the initiator using the insertion jig that has been positioned to the gas generator attachment portion and then install the initiator in the housing. By positioning the initiator and then installing it in the housing, the orientation of the electric conductive terminals of the initiator becomes constant. As a result, the lead wire can be drawn in a fixed direction, allowing a reliable connection of the initiator and the sensor with the lead wire. With respect to the positioning of the initiator, aside from using the insertion jig as described above, the initiator can also be positioned by forming, for instance, a groove or protrusion in the storage opening for storing the initiator and also forming, on the outer circumferential surface of the initiator or the initiator collar provided at the lower portion of the initiator collar, a protrusion or groove which complementarily fits the groove or protrusion formed in the above-mentioned storage opening for the initiator, and then fitting them together.
In the present invention, except for the initiator and initiator collar, any conventionally used elements required to operate the gas generator, such as a xe2x80x9chousingxe2x80x9d having gas discharge ports, xe2x80x9cgas generating meansxe2x80x9d for generating gas by combustion, xe2x80x9cfilter meansxe2x80x9d for purifying and cooling the generated gas, can be used. Further, other structures and members for an air bag gas generator advantageous to the operation of the air bag gas generator, such as: an xe2x80x9cinner cylindrical member,xe2x80x9d which partitions the inside of the housing into two or more chambers; a xe2x80x9cfilter support member,xe2x80x9d which is provided between the inner cylindrical member and the filter means, and which supports the filter means; xe2x80x9cshort-pass preventing means (plate member, etc.),xe2x80x9d which encloses the top end and/or bottom end of the inner circumference of the filter means and which prevents the gas generated from passing through the gap between the filter means and housing inner surface; a xe2x80x9ccushion member,xe2x80x9d which is provided above and/or below the gas generating means to prohibits the gas generating means from moving; a xe2x80x9cperforated basket,xe2x80x9d which has multiple holes, is cylindrical in shape, and is provided on the inner side of the filter means to prevent the gas generating means from directly contacting the filter means and to also protect the filter means from the flames from the combustion of the gas generating means; and a xe2x80x9cplenum,xe2x80x9d which is provided between the outer surface of the filter means and the inner surface of the side wall of the housing and which functions as a gas channel, can be used as desired.
The housing can be formed by casting, forging, or press work, etc. The housing is preferably formed by welding a diffuser shell having gas discharge ports and a closure shell having the igniting means storage hole. The two shells can be joined by various welding methods, such as: electron-beam welding; laser welding; TIG welding; projection welding; etc. When forming the housing by welding the diffuser shell with the closure shell, the cylindrical member is welded and incorporated into the inner surface of a circular area of the diffuser shell. When the diffuser shell and the closure shell are formed by press-molding steel sheet, such as stainless steel sheets, etc., the manufacture of the two shells becomes easy and a reduction in manufacturing cost is achieved. Also, by forming the two shells into simple cylindrical shapes, the press-molding becomes easy. As for the material for the diffuser shell and closure shell, stainless steel sheet is desirable, but nickel-plated steel sheet may be used.
In the air bag gas generator of the present invention, in particular, positioning of the initiator is performed. Therefore, an electrical ignition type, which is activated by an electrical signal transmitted from an impact sensor sensing an impact, is used as the igniting means. This electrical ignition type igniting means comprises: an electrical sensor, which senses an impact exclusively by means of an electrical mechanism; and an initiator, which is activated by an electrical signal from the electrical sensor sensing an impact. For this electrical sensor, there are, for instance, a semiconductor-type acceleration sensor, etc. The semiconductor-type acceleration sensor has four semiconductor strain gauges formed on a silicon substrate beam, which is designed to be deflected when acceleration occurs. These semiconductor strain gauges are bridge connected. When acceleration occurs, the beam is deflected, and the surface is strained. Because of this strain, the resistance of the semiconductor strain gauges changes, and this resistance change is detected as a voltage signal that is proportional to the acceleration. In the electrical ignition type igniting means, in particular, a control unit, further having an ignition evaluation circuit, may be included. The signal from the above-mentioned semiconductor type acceleration sensor is inputted in the ignition evaluation circuit. The control unit begins its calculation at the point at which the impact signal exceeds a certain value. It, then, outputs the activation signal to the gas generator when the calculation result exceeds a certain value.
As the gas generating means, agents based on inorganic azide which has been widely known in the art, in particular a sodium azide, for instance, an equivalent mixture of soda azide and copper oxide, or a non-azide gas generating agent can be used. Various non-azide gas generating agent compositions have been proposed. For example, known compositions are ones primarily composed of an organic compound containing nitrogen, such as tetrazole, triazole, or the metal salts of these, etc., and an oxidizing agent containing oxygen, such as alkali metal nitrate, etc., and compositions using as their fuel and nitrogen source triaminoguanidine nitrate, carbohydrazide, nitroguanizine, etc., and using, as their oxidizing agent, the nitrate, chlorate, perchlorate, etc., of an alkali metal or alkali earth metal. Any one of these agents, but not limited thereto, may be used as the gas generating means in the present invention. They are selected as needed according to the burning rate, non-toxicity, and combustion temperature requirements. The gas generating means is used in the appropriate shape, such as a pellet, a wafer, a hollow cylinder, multiple holes, a disc, etc.
The filter means, which is accommodated and installed in the housing, is approximately cylindrical in shape. The filter means removes combustion residues produced by the combustion of the gas generating means and cools the combustion gas. As for the filter means, a filter for purifying the generated gas and/or a coolant for cooling the generated gas, which are known in the art, can be used. Aside from these, a laminated wire mesh filter, etc., formed by compression-molding a ring-shaped laminated form of wire mesh composed of an appropriate material, may also be used. More specifically, the laminated wire mesh filter can be formed by: shaping a plain stitch stainless steel wire mesh into a cylindrical body; forming a ring-shaped laminated shape by repeatedly bending one end of the cylindrical body outward; and compression-molding this laminated body in a mold. It may also be formed by shaping a plain stitch stainless steel wire mesh into a cylindrical body, forming the cylindrical body into a sheet by radially pressing the cylindrical body, forming a laminated body by rolling this sheet many times into a multi-layer body to form a cylindrical shape, and compression-molding the laminated body in a mold, etc. The material used for the wire mesh may be stainless steel, such as SUS304, SUS310S, SUS316 (JIS standard code), etc. SUS304 (18Cr-8Ni-0.06C) stainless steel exhibits excellent corrosion resistance as does austenitic stainless steel.
The filter means can also employ a dual structure, having an inner layer or an outer layer composed of a laminated wire mesh body. The inner layer may have a filter means protection function for protecting the filter means against the flame from the igniting means bursting toward the filter means and also protecting the filter means from the combustion gas generated by the gas generating means. The outer layer may have a filter means expansion-suppressing function to prevent the plenum formed between the filter means and the outer wall of the housing from being blocked by the expansion of the filter means due to the gas pressure generated when the gas generator is operated. Incidentally, the function to prohibit expansion of the filter means can be achieved by supporting the outer circumference of the filter means with an outer layer made of a laminated wire mesh body, a perforated cylindrical body, a ring-shaped belt body, etc.
The above-mentioned gas generator for an air bag is placed inside a module case along with an air bag that is inflated by introducing the gas generated by the gas generator to constitute an air bag system.
In the air bag system, coupled with the impact sensor, the gas generator is activated and combustion gas is discharged from the gas discharge ports in the housing. The combustion gas is discharged into the air bag, and because of this, the air bag ruptures the module cover and inflates. This creates a cushion for absorbing the impact between hard structures and a passenger inside a vehicle.
In the present invention, by positioning the initiator and then installing it in the housing, the orientation of the electrically conductive terminals of the initiator is fixed. As a result, the lead wire, which is connected to the terminals, can be drawn in a specified direction.
In the gas generator of the present invention, the lead wire can be drawn in a specified direction; thus, installation of the gas generator to the module can be performed reliably with good reproducibility.